Driven both by the needs of users and the capabilities of various implementation technologies, computers and the ways that people interact with them are redesigned again and again.
In doing so, it is desirable to optimize the design of each system according to the current technology and current understanding of human factors. However, another, often opposing, force shaping the design of computer systems is the need for new systems to be capable of utilizing preexisting components, both hardware and software. This force flows from various sources, including the desire to continue to exploit large investments in pre-existing designs, and the desire to use new systems in environments that continue to be populated with preexisting systems.
It is particularly advantageous for a new system to be able to utilize preexisting software components, both application programs (programs that adapt a system to address real world tasks--often, referred to simply as "applications") and system programs (providing system management functions and services used by application programs). Because some preexisting applications have become de facto standards within certain user communities, it is of particular importance that a new system be able to run these standard applications.
Most software that provides for user interaction, is designed for primary user input in the form of keystroke data. A growing body of software, especially that designed for desktop systems, accepts input from a mouse, in addition to keystroke data; generally, these systems still require keystroke data for certain functions.
To make computer systems easier for people to use, various systems have included stylus-type input devices (typically used with a digitizing tablet). Because of their similarity to conventional writing implements, stylus-type devices are, among pointing devices, particularly well suited to be used for character input, in addition to functioning as a pointing device. When used, stylus-type input devices have generally been provided in addition to a keyboard. In some cases, systems have been designed with a stylus-type device as the primary user input device.
A keyboard has characteristics that differ radically from those of a stylus and digitizing tablet. With a keyboard, precise character identification is straightforward: a user generates data representing alphabetic characters simply by pressing corresponding keys. Because a keyboard can be used to create a character with a single event (i.e., press of a binary switch), all the feedback to the user that is needed is display of the character and perhaps accompanied by an audible click. In contrast, while a stylus can be used for character input, very different feedback to the user is required. Handwritten characters are generated by a process that (although familiar to a user) is much more complex, both for the user and for the computer system.
For making function selections with a keyboard, a wide range of alternative approaches are used; of these, pointing to a visible representation of a function or object to be manipulated is awkward, because a keyboard is a very poor pointing device.
A mouse is often used in systems that permit a user to use the mouse to drag objects on the screen. This is accomplished by providing display of a particular type of mouse cursor or pointer: this cursor has an absolute location known to the system, and the system adjusts the cursor's location according to relative movements of the mouse; this cursor functions as an absolute intermediary between the relative movements of a mouse and the object drag operations.
If programs designed to use a mouse cursor are used with a stylus that operates directly on the display screen, the user might expect to be able to directly manipulate the cursor with the stylus, i.e., by placing the stylus over the cursor and dragging it. Typically, this works in a way that users are likely to find frustrating: the relationship between an amount of mouse movement and the distance moved by the cursor is not fixed; this may vary from application to application or even vary within a single application (e.g., it may be a function of velocity); as a result, although the stylus may start on the object, the object will not track the position of the stylus.
In a system in which a stylus is used, it is particularly advantageous for the user to be able to use the stylus directly with the display. For example, it should be possible to write directly on the display screen, and, when appropriate, a trail of "ink" should appear on the display in the path taken by the stylus, thus appearing to a user much like writing on paper.
A pointing-type input device to be used directly on a screen should provide its absolute position (so that the ink appears on the screen at the location of the stylus). This differs from the input provided by a mouse, which provides relative position: with a mouse, the user can generate mouse data indicating nothing but a series of rightward movements, and still have the mouse end at its starting location (e.g., move a mouse to the right, pick up the mouse, place it to the left of its original position, and move the mouse to the right to return to the original location). Thus, although both a mouse and a stylus are "pointer-type" devices (locators), their characteristics differ.
The input of character codes presents another type of impediment to running preexisting (non-stylus) programs with a stylus. Input of handwritten characters is a sufficiently complex as to require feedback to the user. Yet a program not contemplating handwritten input wig have defined a user interface with no provision for such feedback.
These differences in input device characteristics are major impediments to effective utilization of much existing software with a stylus-based computer system. As result, the practice has been that most of the uses of stylus-based input have relied upon application programs written specifically for a system that includes a stylus.
A system built according to the present invention can run preexisting software and permits a user of the system to use a stylus to interact with such software.